The present invention relates generally to landfill metering devices, and more particularly to devices for measuring the flow of gases from landfills through gas extraction wells.
Waste products decompose in landfills, and after the free oxygen in the landfill is depleted, the waste product decomposition generates methane gas. It is desirable to recover this methane gas for environmental and safety reasons, and because subsequent to recovery the gas can be used as a source of energy.
Accordingly, systems have been developed to extract the methane. One such system is disclosed in U.S. Pat. No. 5,458,006, which discloses that its system and other such systems typically include a plurality of vertical pipes, referred to as xe2x80x9cwell casingsxe2x80x9d, that are vertically advanced at various locations into the landfill. The well casings are perforated along their lower-most segment, so that gas from the landfill can enter the casings. A network of horizontal pipes on or near the surface of the landfill interconnects the well casings, with a source of vacuum being in fluid communication with the network of horizontal pipes to evacuate the network and, hence, to evacuate methane gas from the well casings.
It happens that as methane gas is evacuated from a landfill, oxygenated air seeps back in. To avoid adversely affecting the generation of methane, however, the rate of oxygen inflow to the landfill must be controlled. Stated differently, to ensure continued methane gas production, the rate of gas extraction from the landfill and, thus, the rate of oxygen inflow to the landfill must be established to remain below a predetermined flow rate.
Not surprisingly, the methane gas extraction systems mentioned above typically provide for measuring gas flow rate through the well casings. In response to the measured rate, valves in the systems can be manipulated as appropriate to establish a desired flow rate through the well casings.
Several methods exist for measuring gas flow through the well casings. These methods typically involve measuring gas flow through a metering pipe that is in fluid communication with the well casing. One method simply involves measuring pressure at two points of the metering pipe that are longitudinally separated from each other. As is well understood, pressure head is inevitably lost in a pipe between an upstream location and a downstream location, with the magnitude of the pressure head loss being related to the gas flow rate through the pipe. Consequently, the pressure differential between any two longitudinally-spaced points in a pipe can be measured and then correlated to a gas flow rate.
Other methods for measuring gas flow rates through metering pipes include disposing an obstruction such as an orifice or a pitot tube in the pipe and then measuring the pressure differential across the orifice or at the taps of the pitot tube. The pressure differentials are then correlated to gas flow rates in accordance with widely understood principles. The use of orifices advantageously permits the use of relatively short metering pipes, vis-a-vis metering pipes which simply measure head loss.
With particular regard to orifices, the ""006 patent mentioned above teaches a metering pipe having an upstream segment and a downstream segment, with the segments being joined by a pipe coupler and with only the uppermost end of the downstream segment protruding through a bushing above the well casing. The remainder of the metering pipe, including an orifice used to generate pressure signals for calculating flow rate, is located in the well casing. As contemplated by the ""006 patent, the metering pipe segments are made of polyvinylchloride (PVC), and the coupler is a PVC coupler formed with an internal ridge against which the pipe segments are advanced. The orifice is formed in a separate disc-shaped orifice plate made of plastic or steel which is sandwiched between the ridge of the coupling and one of the pipe segments. Thus, flow through the pipe does not encounter only a flat disc-shaped planar surface of an orifice plate, but the orifice plate circumscribed by the ridge of the coupling which rises from the plane of the plate. The combined effect of the ridge and plate can cause flow turbulence and thus decreased measurement accuracy.
Not surprisingly, therefore, the ""006 patent teaches that the pressure taps which are formed in the metering pipe segments upstream and downstream of the orifice must be longitudinally distanced from the orifice plate by distances that are multiples of the diameter of the metering pipe, to ensure accurate flow rate measurement. For this reason, pressure lines must extend through the bushing, requiring modification of the bushing and rather elaborate pressure line-bushing fittings to ensure that gas does not leak between the pressure lines and bushing. As a further undesirable result, it will readily be appreciated that such a structure inhibits easily raising or lowering the metering pipe as might be required, e.g., to compensate for well casing settling. Like the ""006 patent, U.S. Pat. No. 4,562,744 to Hall et al. teaches that pressure sensors in an orifice meter must be distanced from the orifice plate such that xe2x80x9cminimum swirl or turbulence existsxe2x80x9d. As recognized by the present invention, however, a metering pipe orifice plate in combination with an internally ridged PVC coupling need not create turbulence. Further, the present invention recognizes that upstream and downstream pressure taps in a metering pipe containing an orifice need not be distanced from the orifice, but may be formed adjacent the orifice, thereby simplifying construction and design of the flow metering device while still ensuring accurate flow measurement.
Still further, the present invention understands that an easy and desirable way to engage flow sensor connectors to the ports of an orifice system is by threaded engagement. However, we have discovered that for some pipe sizes, the wall thickness is not sufficient to securely maintain and/or support the threaded engagement. The present invention addresses this problem.
A pipe coupling includes a single unitary hollow, preferably PVC body defining a fluid entrance segment and a fluid exit segment. An orifice plate is disposed in the body between the segments. The orifice plate defines an orifice and is made integrally with the body. Thus, the orifice plate and body preferably are one single unitary structure. An upstream port is closely juxtaposed with the orifice plate between the plate and the fluid entrance segment, and a downstream port is closely juxtaposed with the orifice plate between the plate and the fluid exit segment. As intended herein, the ports are configured for engaging respective flow rate metering connectors.
In the preferred embodiment, the coupling defines a longitudinal axis and the orifice defines a center that is distanced from the axis. Preferably, the ports are formed in the PVC body opposite the orifice relative to the axis.
In accordance with the present invention, the ports are internally threaded, to engage threaded flow sensor connectors. To support threaded engagement in the case of smaller couplings, the fluid entrance and exit segments of the coupling can define a first wall thickness, with the body including a port section between the entrance and exit segments and defining a second wall thickness greater than the first wall thickness. The ports are formed in the relatively thick port section. For butt-weld couplings, the port section has the same inner diameter as the fluid entrance and exit segments and a greater outer diameter, whereas for couplings designed to receive pipe segments in a surrounding relationship, the port section has the same outer diameter as the fluid entrance and exit segments, but a smaller inner diameter.
In another aspect, a fluid flow rate metering device includes an orifice plate defining an orifice and a plastic pipe body made integrally with the orifice plate. Threaded upstream and downstream sensor ports are formed in the body upstream and downstream, respectively, of the orifice plate for engaging connectors of a fluid flow rate sensor.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: